Pumps of the above mentioned kind can roughly be divided into two types: centrifugal pumps and axial pumps.
The centrifugal pump comprises an impeller consisting of a hub and at least one cover disc with a number of vanes arranged to the hub, a so called open impeller. A so called closed impeller is arranged with two cover discs with vanes between. The liquid is in both cases sucked in axial direction in the centre of the impeller and leaves the impeller at the periphery in mainly tangential direction.
The axial pump differs from the above mentioned centrifugal pump in that the liquid leaves the pump mainly in axial direction. This deflection is done with the aid of a number of guide rails arranged downstream in the pump housing. The guide rails normally also serves as supporting elements in the construction of the pump housing.
During pumping of polluted liquids such as waste water, water in mines, at construction sites etc, the pumping is often disturbed by the pollution. This may cause clogging of pump impellers and pump housings and also often lead to considerable wear problem.
During pumping of waste water that may contain elongated objects such as rags, there are several methods for solving the problem. An open pump impeller with only one cover disc is then preferred, but even so external measures are required. One may be to run the pump impeller backwards at certain intervals. Another is to arrange some sort of cutting means in front of the intake. U.S. Pat. No. 5,516,261 discloses an open pump impeller for pumping of waste water where the bottom of the pump housing is arranged with a spirally shaped groove, which leads pollutants out towards the periphery where they can cause less damage.
During pumping where high lifting heights are required, for example in mines, closed pump impellers are used, i.e. such with two cover discs, an upper and a lower as well as intermediate vanes. Such impellers have generally speaking higher efficiency than open impellers at high pressure heights. On the other hand, closed impellers have a lesser lead-through, which means higher risk for clogging.
The pollution that is present during pumping in mines often contain elements of highly abrasive material, implying that the material in both pump impeller and pump housing are exposed to great stress. These problems can partly be solved by special surface treatment or hardening of the different components, but it is naturally a desire to ensure that the abrasive particles leave the pump housing as fast as possible in order to avoid unnecessary wear. Further, the geometrical design of the parts that are important for the pumping function of central importance in order to reduce the wear.